Hydrogenated nitrile rubbers offer the advantage of being resistant to oxidative degradation at high temperatures and also offer outstanding oil resistance. By virtue of these properties hydrogenated nitrile rubbers have excellent characteristics for utilization in applications where high temperatures and organic solvents, such as oils, are encountered. For instance, hydrogenated nitrile rubbers are frequently utilized in automotive applications where it is critical to have good heat resistance and good oil resistance. Accordingly, hydrogenated nitrile rubbers are frequently employed in belts, seals, gaskets, and hoses for internal combustion engines.
Hydrogenated nitrile rubber is made by hydrogenating the double bonds of conventional nitrile rubber. U.S. Pat. No. 4,452,950 discloses a process for hydrogenating the double bonds in a nitrile rubber while it is in latex form. The process of U.S. Pat. No. 4,452,950 is carried out in the presence of hydrazine, an oxidizing agent, and a metal ion initiator. Unfortunately, it is expensive to hydrogenate the double bonds of a nitrile rubber regardless of the specific hydrogenation procedure used. Hydrogenated nitrile rubber currently sells at a price of about $12-14 per pound. High cost has greatly limited the commercial utilization of hydrogenated nitrile rubber even though it has excellent physical and chemical properties for a wide variety of applications.
Sunigum.RTM. rubber is currently being sold by The Goodyear Tire & Rubber Company at a small fraction of the price of hydrogenated nitrile rubber. Sunigum.RTM. rubber is comprised of repeat units which are derived from (a) butyl acrylate, or optionally a mixture of butyl acrylate and 2-ethylhexyl acrylate containing up to about 40 percent 2-ethylhexyl acrylate, (b) methyl methacrylate, ethyl methacrylate, methyl acrylate or ethyl acrylate, (c) acrylonitrile, (d) styrene, and (e) a crosslinking agent. Rubbery polymers of this type can be made by utilizing a free radical emulsion polymerization technique, such as the technique described in U.S. Pat. Nos. 5,380,785, 5,616,651, 5,674,933 or 5,767,173.